WGS 84 Earth Gravitational Model

The Geosciences Division

This division in the Office of Geomatics at NGA is responsible for collecting, processing, and evaluating gravity data (free-air and Bouguer gravity anomalies). These data are then used to compute gravimetric quantities such as mean gravity anomalies, geoid heights, deflections of the vertical, and gravity disturbances. All of these quantities are used in World Geodetic System 1984 support, navigation systems, mapping projects, and different types of surveys.

EGM2008

EGM2008 is available for use by the Department of Defense. However, NGA is developing a comprehensive Earth Gravitational Model Implementation Plan for use within the National System for Geospatial-Intelligence. The Implementation Plan will include specific data, format, file and algorithm guidance for system developers on EGM2008 and future geoid releases.

The official Earth Gravitational Model EGM2008 has been publicly released by the NGA EGM Development Team. This model is complete to degree and order 2159, and contains additional spherical harmonic coefficients extending to degree 2190 and order 2159. Full access to the model's coefficients and other descriptive files with additional details about EGM2008 are provided from the link below.

EGM96 and EGM84

The Geosciences Division provides the normalized, geopotential coefficients for both the new NGA/NASA EGM96 n=m=360 and the WGS 84 n=m=180 Earth Gravitational Model. It also provides two geoid products, the 15-minute, worldwide geoid height file for EGM96 and the 30-minute worldwide geoid height file for the original WGS 84 model. Both the EGM96 and the WGS 84 geoid height files and coefficient files have associated software and documents. They are available for unlimited distribution. The NGA/NASA 15-minute worldwide geoid height file and the WGS 84, n=m=360, EGM96 coefficient file are approved for official DoD use as documented in NGA TR8350.2, Third Edition, 4 July 1997. The 30-minute geoid height file and the WGS 84, n=m=180, EGM coefficient file described on the WGS 84 (180,180) web pages are approved for DoD use as documented in DMA TR8350.2, Second Edition, 1 September 1991.